Microprocessor is a device that integrates the functions of the central processing unit (CPU) of a computer onto one semiconductor chip or integrated circuit (IC). Microprocessor contains the core elements of a computer system, and is the computation and control engine of the computer system. Only a power supply, memories, peripheral interface ICs, and peripherals (typically input/output and storage devices) need be added to build a complete computer system.
A microprocessor consists of multiple internal function units, such as: an arithmetic logic unit (ALU), control units, memories, memory interfaces between external and internal memories, interrupt or exception controllers, and internal caches. Other function units that assist in floating-point match calculations, program branching, or vector processing may also be included. The function units of the microprocessor work independently or interact with one another to complete tasks.
Multiple function units share and access resources, such as memories, caches, on the microprocessor in order to complete tasks. When multiple function units need to access a shared resource at the same time, an arbiter is needed to decide which function unit will access the share resource first, or second, etc. Tasks performed by some function units are considered to have higher importance (or priority) than tasks performed by other function units. The requests to access the shared resources by these function units of higher importance should be granted before the requests from than the function units with less importance. However, granting accesses to the requests from function units with high importance before granting accesses to the requests from function units of less importance could lead to starvation of access opportunities to the shared resources of requests from function units with less importance (or priority).
As a consequence, there is a need for an arbiter in a microprocessor that can handle requests from function units with different priorities without starving the access opportunities of requests from function units with low priority.